Acquisition and transmission of multidrug-resistant organisms (MDROs) in healthcare facilities is a major patient safety problem, afflicting in particular the antibiotic-exposed and immunodeficient patient populations. MDRO-colonized patients require isolation to reduce the risk of transmission to other patients, and frequently develop infections from their colonizing organisms. Most clinically relevant MDROs are carried in the gastrointestinal tract; thus perirectal cultures are frequently the surveillance method used to screen for these pathogens. Surveillance to identify MDRO colonization allows for anticipation and timely initiation of effective treatment of patients who develop infection. The precise modes of transmission within hospitals are not known, but contamination of the hands of healthcare personnel, patient care equipment, and the healthcare environment are thought to play major roles in transmitting MDRO. Suboptimal hand hygiene can lead to transmission on the hands of staff to other patients or colonization of their own gastrointestinal tract. Few studies have investigated intestinal colonization of healthcare professionals. Transmission of bacteria by healthcare personnel is thought to occur primarily via contaminated hands; we wonder whether gastrointestinal carriage by healthcare personnel also plays a role in nosocomial spread. This study will screen a self-referred convenience sample of 400 healthcare personnel who have contact with patients or patient culture specimens for fecal carriage of MDRO at one point in time. A control group of 400 NIH employees or contractors who do not have contact with patients or patient specimens will also be screened. Samples will be linked to questionnaires to assess the exposure of staff members to patients or culture specimens with known MDRO colonization or infection. We will use molecular typing techniques to link healthcare personnel isolates to patient or environmental isolates. Finally, the study will be conducted in such a way as to preserve to the greatest extent possible the anonymity of volunteers, using a system of alphanumeric identifiers and unmanned drop boxes for specimen collection.